In the production of many work pieces, it is necessary to employ tubing having one or more holes formed or cut in the side wall. In the past, it has been the practice to cut holes in the side wall of the tubing from the exterior. This has been accomplished by drilling the holes or by forcing a punch inwardly against the side wall of the tubing. In both of these practices, a flange or burr is formed in the interior of the tube requiring additional steps to clean the opening of these formations. Additionally, when the aperture is formed from the exterior of the tube, punching or cutting the hole often results in deformation of the tube.
Openings in the side wall of tubes have also been formed from the interior of the tube. Two methods of forming such openings in tubes re shown in the patent to K. W. Klinksiek, U.S. Pat. No. 3,271,988, issued Sept. 13, 1966 and the patent to J. R. Griffin, U.S. Pat. No. 3,259,003, issued July 5, 1966. The Klinksiek patent discloses a method for using a ram with an inclined ramp for forcing a punch against the side wall of a hollow work piece. Although the aperture is formed from the interior of the work piece, the connecting structure between the ram and punch are nonsymmetrical about a plane through the center line of the punch and ram. Thus, the punch is loaded off-center causing irregular punch action.
The Griffin reference employs a much different approach wherein a plurality of punches are mounted on a shaft which is raised by the action of an inclined second shaft moving relative to the punch shaft.
It has also become important to provide proper dimensioning apparatus such that a plurality of holes may be formed sequentially in a tube without requiring the work piece to be remeasured for each opening formed. At the same time, a means for providing outside wall support around the area to be punched by the apparatus has been needed.